Abu Dawud Book 35, Hadith Number 4705.
Narated By Al-Abbas ibn AbdulMuttalib : I was sitting in al-Batha with a company among whom the Apostle of Allah (PBUH) was sitting, when a cloud passed above them.
The Apostle of Allah (PBUH) looked at it and said: What do you call this? They said: Sahab.
He said: And muzn? They said: And muzn. He said: And anan? They said: And anan. AbuDawud said: I am not quite confident about the word anan. He asked: Do you know the distance between Heaven and Earth? They replied: We do not know. He then said: The distance between them is seventy-one, seventy-two, or seventy-three years. The heaven which is above it is at a similar distance (going on till he counted seven heavens). Above the seventh heaven there is a sea, the distance between whose surface and bottom is like that between one heaven and the next. Above that there are eight mountain goats the distance between whose hoofs and haunches is like the distance between one heaven and the next. Then Allah, the Blessed and the Exalted, is above that.